Method and apparatus for cracking oils



June 16, 1925.

J. G. DAVIDSON METHOD AND APPARATUS FOR CRACKING OILS Filed Nov. 30, 1921 Patented 'AJune 16V, 1.9.25.

AUNITED STATES I 1,-'54L905l luvrsla'rl OFFICE.

JOSEPH GEORGE DAVIDSON, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOB TO U. H.

CONNER, OF NEW YORK, N. Y. 4

mirrnon AND APPARATUS non. cnaoxINeoILs.

Application led November 30, 1921 Serial No. 518,786.

To all-.whom z't may concern.' i

Be .it known that I, J osnrn GEORGE DAVIDSON, a citizen of the United States,

. ing4 Oils; and I do hereby declare the followin to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to any improved method and apparatus for the thermal decomposition or cracking of oils, such as the higher boiling petroleum fractions, etc., for the production therefrom of gasoline and l other products.

More particularly the present invention relates to improvements in .the thermal decomposition or cracking of oils with internal heating of the oil by .electrically heated resistors submerged therein.

The successful cracking of oils by heating the oils internally with electrically heated resistors requires the use of resistors which will carry a heavy current. In using large carbon resistors to heat the oil I have found that a deposit of carbon takes place on the resistors which increases their cross section, thereby reducing the resistance and permitc ting an increased current to flow. If this de Osit is permitted to increase to any considrable extent, I have found that it is practically impossible to separate it from the resistors Without breaking the resistors and making them unavailable for further use, thus making necessary the provision of new resistors of appropriate size for the further carrying out of the process. This injury to the resistors is apparently due to the heavy and firmly adherent layer of carbon formed around the resistor and to the heating of the resistor itself to a higher temperature than that of the surrounding carbon layer, so that, when 4the resistor is cooled the tendency of the resistor to contract is resisted by the surroundin carbon layer with resulting cracking of t e resistor transversely, due to the excessive ten'- sion caused by the contraction.

According'to the present invention, i11- stead of using large resistors and attempting to remove the objectionable carbon deposit therefrom, I take advantage of this carbon deposit and utilize itin forming a resistor of appropriate size within the body of the oil. In order to take advantage ofl this carbon deposit, I make use of a smalll re` sistor as a nucleus and I so carry out the heating of the resistor and of the oil that the deposit of carbon, which, at rst, is of a somewhat mushy consistency, undergoes further change upon continued heating and L forms a resistor of increasing size., In cone junction with this building up of the resistor upon a small'nucleus I make use of suitable regulating means that will so` reduce the voltage as the area of theresistor increases that the input (that is, the voltage timesthe current) remains constant so as to maintain practically a constant heating of the oil during the cracking process. That i's, as the resistance of' the resistors decreases, due to building up of the size of the resistors, I reduce the voltage `so as to obtain the desired heating effect, thereb avoiding the greatly increased heating e fect which would result with increased'cur rent at the same voltage.

The present invention accordingly avoids the necessity for removing the deposited carbon, deposited during the crack-ing operation, but takes advantage of this deposlt for producing the resistors themselves which are used in the carrying out of the cracking operation. The provision of expensive resistors of large size at the outset of the process is thus made unnecessary. At theI endof the cracking operatiomand after the vresistors have so increased in size that they lbars and for. supp ying a heavy current thereto,'and I space these nuclei apart so as to ermit the building up of relatively large and heavy resistors therefrom without short circuiting.

In conjunction with the cracking still I also rov1de means for varying and regu1at' ing t e current so that, as the resistors increase in size, and as their resistance decreases, a substantially censtant or regulated heating effect can nevertheless be olitained.

The nature and advantages of the invention will more fully appear from the. following more detailedl description, taken in central vertical sec'tion of one form of ap paratuS;

, Fig. 2 is a plan view of the still of gigi?) is an enlarged sectional view taken on the line 3-3 of Fig. 1; and

Figs. 4 and 5 are enlarged detail views slliowing how the resistors may be heldin p ace. A i

In the apparatus illustrated the crack- .ing still 1 isof the horizontal type and ofsuitable size te contain a relatively lar e body of oil. The size of the still is capab e Aas. that of the still or under a .of considerable variation and stills may be used having, for example, a capacity of as much as two thousand gallons or more.

The still illustrated has a suitable valvecontrolled inlet pipe 2 for introducing oil and a valve-'controlled outlet pipe 3 for withdrawing the residue from the still. It has a reflux column or tower or dephlegmwtor 4 operating in a manner.

which will be readily understood. End covers or heads 5 are provided through which access may be had to the inside of thek still. A pyromet'er well 7 is also rovided for enabling the temperature 'of t e oil. to be ascertained. The apparatus may in practice be provided with a condenser (not shown) for condensing the distillate, means for maintaining the desired pressure in the still and in the condenser, and means for supplying a regulated supply of oil tothe stillveither in the form of successive charges or progressively during the cracking rocess. The oil may also be preheated, i desired, before it is introduced into the still. It will -be evident that the oil should be forced into the still at a pressure corresponding to that maintained within the still. The still is well adapted for use atV high pressures inasmuch as the still walls are protected from direct heating by the heating means employed, so that they are not weakened, as are the common externally heated stills. The distillate may be condensed either under the same high pressure ower pressure. The still is provided with resistors adapted to be heated by a three-phase alternating current. One suitable means of introducing the current and of connecting amanece the resistors is illustrated in Fig. 3. l The still is provided with an opening 8 arranged with 'a stungbox and tapered to accommodate the concentrically arranged conical members 9, 10 and 11 to which the leads of the three phases of the current are connected, and which are insulated from each other and from the still walls by suitable insulating means arranged, for example, in the manner illustrated.

This arrangement of the leads reduces hysteresis losses to a minimum. Furthermore, the necessity of spreading three stuifing boxes on the top of the sti l is avoided, the stuffing box shown being only slightly larger than would be necessary for each lead if they were brought in separately. By

constructing the leads 9 and 10 as cylindrical or frustro-conical shells 1 utilize the so-called skin eect which causes alterhating currents to flow at or'near the surface of the conductor, the central portions of the said conductor carrying only a very smally portion of the total current. The supporting and connectin members 12, 13, and 14 are united, respectively, to the members 9, 10 and 11 and are connected at their lower ends with the supports 15 of the rods 16, one of which is illustrated in Fig.

4. At their other ends, the rods 16 are supported on supports 17 which are in turn supported from the still walls by the conductin cross bar 18 and the insulating upright ars 19, and the members 17 are electrically connected together by the cross bar. A modified form of support for holding two superposed rods 24 (instead Vot' one rod 16) is illustrated in Fig. 5, in

which the base member 17n has a depression for receiving the lower half of one oi the rods and the upper member 25 is 'secured thereto by bolts 23 and is also so sha ed as to receive the upper rod 24 and hol it in place by means of the pins 27 operating in openings in the member 25. In orderA to prevent carbon deposit upon the heads of the screws 23 and to permit ready removal of these screws even after a deposit of carbon has taken place on the rods 24, insulating caps 26 may be arranged over the heads of these screws.

It will thus be seen that the construction i's such that the rods 16-can be readily in- 'Serted and held in lace and also such that,4

when the resistors ve been built up to a large size around the rods 16, they can nevertheless be broken away from the su ports and further nuclei rods inserted. n inserting these' rods a'cement'ing material for example, a mixture of powdered graphite and molasses may be used which, upon passage of the current, 'ves a good electrical connection between t e rods and their sudpports through which the current is supplie lll() In order to permit a deposit of carbon to be formed, upon the nuclei rods and to increase so as to form large resistors, the nuclei rods or bars are spacedapart from the still walls and from each other so that the carbon deposit will be prevented from bridging across until the resistors have increased to a large size.v

In the operation of the apparatus and the carrying out of the cracking operation I introduce one or more thin rods or bars, depending upon whether an alternating or direct current is used, or whether a singlephase or polyphase alternating current is used, and connect theserods with the leads for the electric current, for example, in the manner illustrated and above described. By using as a nucleus or as nuclei a thin rod or rods of about one inch in diameter by eighty inches long, these rods can be heated by the use of a heavy current so that. a layer of carbon will begin to build up on the rods quite rapidly. This carbon deposit will result in an increase in the current conducting area of the rod. As the diameter of the rod increases, due to the deposit of the conducting carbon, the volta e can be lowered to maintain a constant oad, that is, the voltage can be lowered as the current increases, this latter being due to the decrease in resistance, so that the heating effectv will remain approximately constantA or within predetermined limits. The process can be continued in this way until the deposit .y of carbon upon each rod becomes thick enough to cause short-circuit. The accumulated carbon of the resistors can then be removed and further nuclei introduced.

The regulation of the current can be effected by suitable regulating means, and this regulation may be automatic in character. For example, a transformer may be used with regulation of the voltage so that the voltage will drop as the size of the resistor increases, so that the heatingelect, due to the current supplied, will be maintained practically uniform or within the desired limits. If, for example, a current is initially supplied of 2,000 amperes at volts, the voltage can be decreased in proportion to the decrease in resistance so that,

with a current of 4,000 amperes, the volta e will be reduced to about 50 volts. At t e outset a current of from 200 to 1000 amperes per square inch of cross section may be used at a voltage of from 100 to 200 volts. As the cracking operation proceeds and the deposit of the carbon-increases the cross section of the nuclei and thereby decreases their resistance, a current of increased amperage wi-ll tend to pass at approximately the same voltage, but by the use of suitable electric ap aratus the voltage can bev decreased as t e ampe e increases so that the heating ei'ect will be substantially constant, that is, the input of `energy will remain approximately constant and therefore the rate of cracking or of distillation o the oil will remain practically constant or uniform. It will thus be seen that the present invention provides for the carrying out of the cracking operation with regulation and control of the operation, and that advantage is taken of the carbon deposit formed during the cracking operation to produce, within the body of oil, the resistors which are used in the carrying out of the cracking operation, it being necessary merely to provide nuclei at the' outset upon which the building up of the resistors will take place.

From another viewpoint, it may be considered that the present invention involves the production ,of carbon 'from ctroleum of such a character that it is wel ada ted for use in making carbon resistors. at is, the carbon deposited on the nuclei and which forms-the resistors during the cracking operation, is suilicient in amount so that, at the end ot the cracking operation, and when the resistors have built up to 'such a degree that they are to be removed, a considerable amount of carbon is provided which can be broken `upand used for electrical or other purposes, for example, in the making of the nuclei rods or bars used in the process.

I claim".I

1. The method of cracking oils with internal electrical heating vof the oil which comprises supplying the current initially through nuclei resistors and causing the resistors to build up by carbon deposits thereon durin the cracking operation, regulating the e ectric current and decreasin the volta e as the cross sectional area o? the electrlc resistors increases.

2. The process according to claim 1, in which aplurality of nuclei resistors are used andl in which the current is supplied as polyphase alternating current to such resisters.

3. The `process according to claim 1, in which the voltage is so regulated with increase in size of the resistors that a substantially constant heatin eect is obtained.

`4f. An apparatus or cracking oil comprising an oil cracking still, relatively thin nuclei resistors of carbon therein, means for detachably securing the resistors in the still and for supplying electric current thereto,

and means for sup orting the nuclei resistors away from eac other and away from the walls of the still to permit the formation of relatively thick resistors thereon by deposition of carbon.

5. An apparatus for crackin oil comprising an oil cracking still, relatively thin nuclei resistors of carbon therein and means for supporting the nuclei resistors away iis ors, means for supplying alternating current to said resistors com rising a plurality of insulated leads introduced through a single opening in the still, and said resistors being spaced apart to permit the building up of carbon thereon progressively during the cracking operation until large massive resistors are formed by such deposit.

In testimony whereof I ailix my signature JOSEPH GEORGE DAVIDSON. 

